Protein kinases are a family of enzymes that catalyze the transfer of the terminal phosphate of ATP the hydroxyl group of specific tyrosine, serine, threonine, or histidine residues in protein. It is known that such phosphorylation plays a fundamental role in essentially all molecular aspects of cell life including metabolism, cell proliferation, cell differentiation, cell migration, and cell survival, and that protein kinases constitute major pharmacological targets [Schlessinger and Ullrich, Neuron, 9, 383 (1992); Cohen, P. Nat. Rev. Drug Discov. 1, 309-315 (2002); Scapin G., Drug Discovery Today 7(11): 601-611 (2002)].
Of the many different cellular functions in which the activity of protein kinases is known to be required, some processes represent attractive targets for therapeutic intervention for certain disease states. For example, specific protein kinases have been implicated as targets in cancer [Traxler, P. M., Exp. Opin. Ther. Patents, 8, 1599 (1998); Bridges, A. J., Emerging Drugs, 3, 279 (1998)], restenosis [Mattsson, E., Trends Cardiovas. Med. 5, 200 (1995); Shaw, Trends Pharmacol. Sci. 16, 401 (1995)], atherosclerosis [Raines, E. W., Bioessays, 18, 271 (1996)], blood vessel proliferative disorders such as angiogenesis [Shawver, L. K., Drug Discovery Today, 2, 50 (1997); Jackson et al J. Pharm. Exp. Ther. 284, 687 (1998); Folkman, J., Nature Medicine, 1, 27 (1995)], chronic obstructive pulmonary disease, bone disease such as osteoporosis [Boyce, J. Clin. Invest., 90, 1622 (1992), Tanaka et al, Nature, 383, 528 (1996)], psoriasis [(Dvir, et al, J. Cell Biol. 113, 857 (1991)], inflammatory disorders such as arthritis [(Badger, J. Pharm. Exp. Ther. 279, 1453 (1996)], central nervous system disorders such as Alzheimer's [(Mandelkow, E. M., et al, FEBS Lett, 314, 315 (1992); Sengupta, A. et al, Mol. Cell. Biochem. 167, 99 (1997)], pain sesation [Yashpal, K., J. Neurosci. 15, 3263-72 (1995)], autoimmune diseases and transplant rejection [Bolen and Brugge, Ann. Rev. Immunol. 15, 371 (1997)], thrombosis [Salari, FEBS, 263, 104 (1990)], metabolic disorders such as diabetes [Borthwick, A. C. et al, Biochem. Biopys. Res. Commun. 210, 738 (1995)], and infectious diseases (Lum, R. T. PCT Int. Appl., WO 9805335A1 980212), and viral infections [Littler, E. Nature, 160, 358 (1992)].
A partial, non-limiting, list of such kinases includes CDK1, CDK2, CDK3, CDK4, CDK5, CDK6, CDK7, CDK8, CDK9, CDK11, PDK1, PDK2, cRaf1, c-src, abl, Araf, ATK, bcr-abl, Blk, Braf, Brk, Btk, cfms, c-fms, c-kit, c-met, CSF1R, CSK, EGFR, ErbB2, ErbB3, ErbB4, ERK, ERK1, ERK2, Fak, fes, FGFR1, FGFR2, EGFR3, EGFR4, EGFR5, Fgr, FLK-4, Fps, Frk, Fyn, GSK, gsk3a, gsk3b, Hck, IGF-1R, IKK1, IKK2, IKK3, INS-R, integrin-linked kinase, Jak, JAK1, JAK2, JAK3, JNK, Lck, Lyn, MEK, MEK1, MEK2, p38, PDGFR, PIK, PKB1, PKB2, PKB3, PKC, PLK1, Polo-like kinase, PYK2, tie1, tie2, TrkA, TrkB, TrkC, UL13, UL97, VEGF-R1, VEGF-R2, Yes, AKT, and Zap70.
As an example, in cancer cells, IGFR-1 plays a critical role because it contributes to the promotion of tumor growth by inhibition of the apoptosis, transformation, metastasis and induction of angiogenesis through the vascular endothelial growth factor.
In addition to tyrosine kinases, there are serine/threonine protein kinases, that phosphorylate serine and/or threonine residues on proteins. Among them, cyclin-dependent kinases (CDKs) play a key role in regulating the cell cycle machinery. These complexes consist of two components: a catalytic subunit (the kinase) and a regulatory subunit (the cyclin). To date, 13 CDKs have been identified along with 25 cyclin-box-containing proteins [Knockaert, M.; Greengard, P.; Meijer L. Trends in Pharmacological Sciences 23(9): 417-425.] Each kinase associates with a specific regulatory partner and together make up the active catalytic moiety. Each transition of the cell cycle is regulated by a particular CDK complex: G1/S by CDK2/cyclin E, CDK4/cyclin D1 and CDK6/cyclin D2; S/G2 by CDK2/cyclin A and CDK1/cyclin A; G2/M by CDK1/cyclin B, the coordinated activity of these kinases guides the individual cells through the replication process and ensures the vitality of each subsequent generation [Science, 274, 1643-1677 (1996); Ann. Rev. Cell. Dev. Biol., 13, 261-291 (1997); Fischer, P. M. Current Opinion in Drug Discovery and Development, 4(5), 623-634 (2001); Draetta, Trends Biochem. Sci. 15:378-382 (1990); Sherr, Cell 73:1059-1065 (1993)].
An increasing body of evidence has shown a link between tumor development and CDK related malfunctions. Over-expression of the cyclin regulatory proteins and subsequent kinase hyperactivity have been linked to several types of human cancers [Senderowica, A. M., and Sausville, E. A., J. Nat. Acad. Sci., U.S.A. 96, 376-387 (2000); Garrett, M. D., Current Opin. Genetics Devel., 9, 104 (1999); Webster, K. R., Exp. Opin. Invest. Drugs, 7, 865-887 (1998); Jiang, Proc. Natl. Acad. Sci. USA 90:9026-9030 (1993); Wang, Nature 343:555-557 (1990)]. More recently, endogenous, highly specific protein inhibitors of CDKs were found to have a major affect on cellular proliferation [Sherr, C. J., Roberts, J. M. Genes Dev. 13, 1501-1512 (1999); Kamb et al, Science 264:436-440; Beach Nature 336:701-704 (1993)]. These inhibitors include p16 (an inhibitor of CDK4/cyclin D1), p21 (a general CDK inhibitor) and p27 (an inhibitor of CDK2/cyclin E). A recent crystal structure of p27 bound to CDK2/cyclin A showed how these proteins effectively inhibit the kinase activity through multiple interactions with the CDK complex [Pavletich, Nature 382:325-331 (1996)]. These proteins help to regulate the cell cycle through specific interactions with their corresponding CDK complexes. Cells deficient in these inhibitors are prone to unregulated growth and tumor formation.
In addition to treating human cancers, CDK inhibitors could be useful in the treatment of other cell proliferative disorders such as familial adenomatosis polyposis, psoriasis, neuro-fibromatosis, fungal infections, endotoxic shock, vescular smooth cell proliferation associated with atherosclerosis, pulmonary fibrosis, glomerulonephritis, and post-surgical stenosis and testenosis [U.S. Pat. No. 6,114,365].
CDKs are also know to play an important role in apoptosis. Therefore, CDK inhibitors, could be useful in the prevention of AIDS development in HIV-infected patients; inflammatory bowel disease, and diabetes mellitus, dementia, Parkinson's disease, amyotrophic lateral sclerosis, retinitis pigmentosa, spinal muscular atrophy and cerebellar degeneration; myelodysplastic syndromes, aplastic anemia, ischemic injury associated with myocardial infarctions, stroke and reperfusion injury, arrhythmia, atherosclerosis, toxin-induced or alcohol related liver diseases, hematological diseases, for example, chronice anemia; degenerative diseases of the musculoskeletal system, for example, osteoporosis, aspirin-sensentive rhinosinusitis, cystic fibrosis, multiple sclerosis, kidney diseases and pain [U.S. Pat. No. 6,107,305].
Also, it has been discovered that some CDK inhibitors can be used in combination therapy with some other anticancer agents. For example, the cytotoxic activity of the CDK inhibitor, Flavopiridol, has been used with other anticancer agents in cancer combination therapy [Cancer Research 57:3375 (1997)].
In addition, a recent report showed that CDK5 is involved in the phosphorylation of tau protein, and therefore, CDK inhibitors may be useful in the treatment of Alzheimer's disease [J. Biochem., 117: 741-749 (1995)].
This increasing body of evidence has led to intense discovery efforts to search for small molecule inhibitors of the CDK family and their associated regulatory molecules (cyclins) as an approach to cancer chemotherapy [Sausville, E. A., Trends in Molecular Medicine 8(4), S32-S37 (2002); Malumbres, M, and Barbacid, M. Nat. Rev. Cancer 1, 222-231 (2001)].
More than 50 small molecule inhibitors of cyclin-dependent kinases have been identified. These CDK inhibitors all target the ATP-binding pocket of the catalytic site of the kinases. The effects of CDK inhibitors on the cell cycle and their potential value for the treatment of cancer, alopecia, neurodegenerative disorders (e.g. Alzheimer's disease, amyotrophic lateral sclerosis and stroke), cardiovascular disorders (e.g. atherosclerosis and restenosis), glomerulonephritis, viral infections (e.g. HCMV, HIV and HSV) and parasitic protozoa (Plasmodium sp. and Leishmania sp.) has been extensively studied [Knockaert, M. Greengard, P. Meijer L., Trends in Pharmacological Sciences 23 (9), 417-425 (2002); Malumbres, M, and Barbacid, M. Nat. Rev. Cancer 1, 222-231 (2001), Sielecki, T. M. J. Med. Chem. 43, 1-18 (2000)]. Three properties make CDK inhibitors attractive as potential anti-tumor agents. First, they are potent anti-proliferative agents, arresting cells in G1 [Soni, R. J. Natl. Cancer Inst. 21, 436-446 (2001)] or G2/M [Damiens, E. et al. Oncogene 20, 3786-3797 (2001)]. Second, they trigger apoptosis, alone or in combination with other treatments [Edamatsu, H. et al. Oncogene 19, 3059-3068 (2000)]. Third, in some instances, inhibition of CDKs contributes to cell differentiation [Matushansky, I. Et al. Proc. Natl. Acad. Sci. U.S.A. 97, 14317-14322 (2000)].
Despite the significant research efforts and resources which have been directed towards the development of novel anticancer agents and improved methods for treating cancer there remains a need in the art for novel compounds, compositions, and methods that are useful for treating cancer with improved therapeutic indices.